1. Field of the Invention
The present invention relates to methods and apparatus for monitoring the usage of a toothbrush by an individual, and for analysing the data thus obtained to identify incorrect usage.
2. The Related Art
It is well known that many dental problems experienced by individuals who regularly use a toothbrush are associated with poor usage of the toothbrush. For example, even if the toothbrush is used several times each day, due to incorrect brushing habits the brush may always fail to come into contact with certain areas of the teeth. Poor brushing coverage of the teeth may also be caused, or at least exacerbated by the design of the toothbrush.
The present invention aims to provide new and useful methods and apparatus for monitoring usage of a toothbrush.
In general terms, a first aspect of the invention proposes that the position of a toothbrush should be monitored relative to the position of the teeth of an individual (i.e. a human subject). The toothbrush contains a first position sensor, and the output of the sensor is fed to processing apparatus which also receives data output from a second position sensor mounted in fixed relationship to the teeth. The processing apparatus compares the two sensor outputs to monitor the position of the toothbrush relative to the teeth over a period of time. Preferably two second position sensors are provided, each in a fixed relationship to the teeth of a respective one of the subject""s jaws. Preferably, the position of the toothbrush with respect to the subject""s teeth is displayed visually, for example as an image on a screen showing the teeth and the toothbrush in their respective positions, or as an image of the teeth with the track of a point of the toothbrush marked as a path over them. The display may be generated in real time, or subsequently.
Preferably the output of the processing apparatus determines the position of the teeth relative to the toothbrush to a high precision, for example to within a few millimetres. To make this possible, the position of the second position sensor relative to the teeth must be registered. Accordingly, in a second aspect, the invention provides a method of determining the position of teeth relative a position-sensitive probe mounted in fixed relationship to the teeth (e.g. on a location of the jaw). The second aspect of the invention proposes that a third position sensor is located in turn during a period of time on, or more generally in a known positional relationship to, the second position sensor(s) and at least four locations on the teeth (preferably more than 4, e.g. up to 200), the output of the third position sensor being monitored during this time.
The at least four locations may either have a known fixed relationship to the teeth (such as four locations which actually are known to be specific points on the teeth), or they may be locations which are determined by the registration process as described below.
Preferably the locations should be evenly spread over the feature to be tracked covering the extents of the feature.
Note that in some embodiments the third position sensor may in fact be the same position sensor which is used in the first embodiment of the invention, i.e. the first position sensor.
The output of the second and third position sensors over this period (even though both will normally only be registering changes in their absolute position, not position relative to each other) are sufficient to determine the position of the second position sensor relative to the teeth.
In a third aspect of the invention, once data is available, preferably from a method according to the first and second aspects of the invention, indicating over a period of time the variation of the position of the toothbrush relative to the teeth, this data is analysed statistically to determine whether it contains any pattern of usage indicative of poor habitual usage. For example, the invention may include determining for each area of the teeth the frequency with which it contacts the toothbrush and comparing this data to pre-existing information characterising correct usage (e.g. a minimum correct frequency of contact. This may be a single value which applies to all surfaces of all the teeth, or a value which varies with different surfaces and/or with different teeth). Another possible analysis is of the orientation of the toothbrush with time during the tooth-brushing event. In either case, if a discrepancy is noted between correct usage and the observed usage, a warning signal is emitted, or, in embodiments discussed below in which the brushing event is being displayed visually, the colour within the display of any tooth or teeth not being visited could be changed or those teeth made to flash.
Although position information on its own is potentially very useful as described above, the information is yet more useful in combination with other sources of information about toothbrush usage. For this reason, a fourth aspect of the invention proposes that a toothbrush should carry other sensors which are sensitive to factors other than position, such as pressure sensors, pH sensors, etc.
A toothbrush as proposed in the first and fourth aspects of the invention generally requires a means of transmitting its data (e.g. to the processing apparatus). While this can be done within the scope of the invention by an electronic or optical fibre, a sixth aspect of the invention proposes that a toothbrush carries wireless data transmission means, such as a transmitter of electromagnetic (preferably radio) waves. Acoustic waves might also be suitable for this purpose, though they should preferably be at a frequency which is inaudible to individuals. The processing apparatus is provided with a corresponding wireless signal reception device. Similarly, the position sensors (especially the first position sensor) are preferably self-powering devices, meaning that they generate all power required for their operation from their motions due to motions of the subject.
Although the invention has mainly been described above in relation to methods, all features of it may alternatively be expressed in terms of a corresponding apparatus arranged to facilitate the invention. Furthermore, the analysis performed in the methods of the apparatus may be performed by computer software present in a computer program product which is readable by a computer apparatus to cause the computer apparatus to perform the processing.
The term xe2x80x9crelative positionxe2x80x9d of two objects, is used in this document to include the translational distance and spacing direction of two objects (a total of 3 degrees of freedom). However, any measurement of the position referred to herein is preferably accompanied by a logically separate measurement of the relative orientation of the two objects (a further 3 degrees of freedom). For example, the measurement of the xe2x80x9cpositionxe2x80x9d of a toothbrush relative to teeth, i.e. measurement of the three-dimensional location of a notional centre of the toothbrush in reference frame defined by the teeth, is accompanied by a measurement of the angle of orientation of the toothbrush around that centre. Thus, while the position of the toothbrush relative to the teeth shows whether the toothbrush is close to a given tooth, and in what direction it is spaced from the tooth, the orientation of the toothbrush represents which direction any given face of the toothbrush (e.g. the upper surface of the bristle head of the toothbrush) faces in the reference frame of the teeth.
Similarly, each xe2x80x9cposition sensorxe2x80x9d used in this document preferably is not only operative to measure changes in its absolute position, but preferably is also operative to measure changes in its orientation. A variety of sensors are known for this task, such as Minibird sensor sold by Ascension Technology Corporation, P.O. Box 527, Burlington, Vt. 05402, USA, which is only some 5 mm in diameter.
A sensor is said to be in fixed positional relationship to either the upper or lower set of teeth when its position and orientation is fixed in relation to those teeth.
There also exist types of sensors that are sensitive only to their position in space, they do not have an intrinsic orientation which can be reported. Such three degree of freedom sensors my also be used in an alternative embodiment of the invention, since the output from combinations of three such sensors the feature to be tracked can be used to calculate missing orientational information. The sensors must be placed accurately at the known offset to one another. The optimum offset will depend on the geometry of the object being tracked.